Not Applicable.
1. Field of Invention
The present invention relates generally to power conversion and, more particularly, to DC-DC power converters.
2. Description of the Background
DC-to-DC power converters are widely utilized in power supplies to convert an input DC voltage into a specified output DC voltage. For modem low power digital applications, typically DC-to-DC power converters are required to efficiently convert an unregulated input DC voltage of, for example, 48V or 120V, to a substantially constant output voltage as low as 5V, 3.3V, or even 1.5V.
Prior art isolated power converters typically regulate the output voltage of the converter by modulating the pulse width of the primary side input switches. A significant source of inefficiency for power converters, however, results from the turning on of the input switches, which are typically MOSFETs, at other than zero volts. Some of these converter topologies can realize zero-voltage switching of the input switches with duty cycle control, but such topologies are ordinarily limited to single-ended converters or to specialized topologies such as the phase-shifted fill bridge.
For double-ended converters employing a symmetric half-bridge topology, zero-voltage switching cannot be realized when the primary switches are pulse-width modulated. In addition, although highly efficient zero-voltage switching of the input switches for half-bridge converter topologies may be realized by fixing the duty cycle of the primary switches at or near fifty percent, the output voltage of the converter will change proportionally with a fluctuating input voltage, which is unacceptable for most modern applications.
Accordingly, there exists a need to achieve a high efficiency isolating converter with zero-voltage switching that maintains high efficiency regulation of the output voltage.
The present invention is directed to a power converter. According to one embodiment, the power converter includes a symmetrical half-bridge converter. The symmetrical half-bridge converter includes a transformer having a primary winding and first and second secondary windings, a primary circuit coupled to the primary winding, a first rectifier circuit coupled to the first secondary winding, and a second rectifier circuit coupled to the second secondary winding. In addition, the power converter includes first and second buck converters coupled to the half-bridge converter.
According to another embodiment, the power converter includes a first power conversion stage including a transformer, at least two unregulated primary switches coupled to the transformer, a first rectifier circuit coupled to the transformer, and a second rectifier circuit coupled to the transformer. In addition, the power converter includes a second power conversion stage coupled to the first and second rectifier circuits of the first power conversion stage, the second power conversion stage including first and second buck converters.
According to another embodiment, the power converter includes a symmetrical half-bridge converter including a transformer having a primary winding and first and second secondary windings, a primary circuit coupled to the primary winding, a first rectifier circuit coupled to the first secondary winding, and a second rectifier circuit coupled to the second secondary winding. In addition, the power converter includes a first buck converter coupled to the first and second rectifier circuits of the half-bridge converter.
According to another embodiment, the power converter includes a symmetrical half-bridge converter. The symmetrical half-bridge converter includes a transformer having a primary winding and a secondary winding, and a primary circuit coupled to the primary winding. In addition, the power converter includes first and second buck converters coupled to the secondary winding of the transformer.
In contrast to the prior art, embodiments of the present invention provide high-efficiency isolating power converters with zero voltage switching, which at the same time provide high efficiency regulation of the output voltage. These and other benefits of the present invention will be apparent from the detailed description hereinbelow.